1. Technical Field
Embodiments of the invention relate to a wafer polishing apparatus. More particularly, embodiments of the invention relate to a wafer polishing and broken platen belt sensing apparatus adapted to sense when a platen belt has broken.
This application claims priority to Korean Patent Application No. 10-2005-0104767, filed Nov. 3, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Discussion of Related Art
In order to form contemporary semiconductor devices, which are smaller and more densely integrated than ever, very flat wafers are required. A number of flattening methods, such as the spin on glass (SOG) method, the etch back method, the reflow method, etc., have been developed. Each of these methods is designed to flatten and smooth the working surface of a wafer.
During a typical wafer flattening process, mechanical polishing and chemical polishing are combined to produce better results than might be achieved by the use of either polishing type alone, since mechanical polishing alone is generally unable to produce sufficiently flat wafer surfaces and chemical polishing is too slow. Thus, various chemical mechanical polishing (CMP) techniques are used which flatten the surface of a wafer using a combination of the mechanical and chemical polishing effects.
In a typical CMP process, a rotating polishing pad fixed to a polishing table is used in combination with a rotating polishing head to apply regular pressure on a wafer fixed to the polishing head by surface tension or vacuum pressure. That is, the weight and applied pressure of the polishing head force the polishing pad and the working surface of the wafer into contact. A slurry is usually applied to this mechanical process through a very narrow gap between the surface of the wafer and the polishing pad. The mechanical polishing effects of the polishing pad may be enhanced through the introduction of abrasive polishing particles in the slurry, and chemical polishing effects may be introduced through an appropriate selection of chemical ingredients in the slurry.
Obtaining uniform and well controlled rotation of the polishing platen holding the polishing pad is an important aspect of the foregoing CMP process. U.S. Patent Application No. 2003-0128127 A1 discloses one exemplary system adapted to monitor the tension of a robot-controlled platen belt used to rotationally drive a polishing platen. In this conventional system, a belt tension monitor is used. An upper tension limit and a lower tension limit for the platen belt are monitored using the belt tension monitor. This type of monitoring is designed to prevent the platen belt from becoming damaged during operation, and to generally extend the platen belt's useful life.
Although the conventional system monitors upper and lower tension limits, it is not adapted to detect a complete failure of the platen belt. As a result, a platen belt failure (e.g., a break) often causes severe damage to a wafer being processed.